Over boost problem
 

I tryed searcing, nothing of any significants came up. I haven't changed anything all i have is HKS down pipe and 3 in cat back with stock cat. Yesterday i was out playing around an i noticed my boost gauge going a little higher then normal. When i got the car it was a perfect 10-9-10, or in my case .7-.6-.7 bar. Now it's doing a 10-9-12, i boosted once and saw it goto .9 bar and haven't tryed floored it since. I'm at a lose as to what i should check. Thanks for the imput guys.

that's because u've reduced the restrictions in airflow of ur engine

because of the Downpipe and catback.. the exhaust can exit the car much faster

which is causing what's known as "boost creep"

ur 2 solutions are

a.) live with the creep and get an ecu to compensate for the extra fuel

b.) remove the turbo's and port the wastegates, so that the exhaust can be bypassed at a greater rate, therefore keeping the boost down

The thing is the i bought the car with the hks down and the cat back and it didn't do that, now it does?

WRONG! Please don't give out extremely bad advice like that....a downpipe and catback may result in higher boost levels but not boost creep. A boost controller or different restrictor pills would easily control the boost to whatever level you like (above 7 psi).

The first thing to check would be the vacuum line leading to the wastegate actuator.

forgive my ignorance, but i'm pretty sure that's the case. (at least in the 4 turbo cars i've owned)

how would the boost go up if it's not through boost creep :Wconfused

when u restrict the exhaust.. the wastegate is the "path of least resistance"

but suddenly when u have a 3 inch sewer pipe and low back pressure.. the "small" wastegate hole is no longer the path of least resistance.. so the air passes throught the turbine and the exhaust rather then the WG

it happend on my FC and on my FD (infact that's how i popped the seal on my FD from boost creep)


what about the whole 3 mod rule for the FD?

the guy doesn't hit 12-10-12 or something he hits 12 at the very top of the power and subsequently where the exhaust flows is highest and the wastegate has to work hardest (and gets over run easiest)

that's why the stock gate just is not adequate on a free flowing intake/exhaust.. it gets even worse with more mods... see what happens if u put a Intake, intercooler, DP MP and CB... if u tell me that aint boost creep...your lying


can u plz explain where my logic is flawed, and why porting my wastegates has worked for me in the past in solving this sort of issues...


how long ago was that? and how much colder has the weather gotten since u bought it? i've noticed my boost rise a couple psi in colder weather also

I've have the car for 6 months and it was about 70 out yesterday when it did this. I've had colder mornings back about 4 weeks and it didn't overboost.

I check the vacume line to the wastegate it's perfectly fine.

You're wrong. :)

The boost level goes up because the stock ecu does not use closed-loop to control boost. It has a set duty cycle to activate the wastegate, which works with the stock system. Once you start modifying the car, this fixed duty cycle is no longer adequate. A boost controller will allow control of the wastegate, which will allow you to control boost to what you want.

Elevated boost is NOT boost creep. Boost creep only occurs when the wastegate is completely overwhelmed and cannot flow enough excess exhaust to control boost. This does not happen on an FD until a full exhaust (with midpipe) and intake is installed. Even then, some cars do not experience it.

That's why your advice was poor. He is experiencing a simple problem with his boost control, not boost creep.

Um, it was proven wrong about 4 years ago. Feel free to read any of the numerous threads on the topic:

https://www.rx7club.com/3rd-gen-archives-73/stock-ecu-10-psi-myth-308996/
https://www.rx7club.com/showthread.p...&highlight=ecu

Those are a start. My wideband results from a downpipe/catback car on the stock ecu were at 10:1 AFR for most of the rpm range.

Then check the wastegate controller solenoid and vac lines.

http://i31.photobucket.com/albums/c3...93vachoses.jpg

From what I've read on the board and on my car, adding a DP and CB can give you boost SPIKE. Which is different from creep, and can be cured with a boost controller.

Listen to Rynberg, you dont have boost creep(no mp) so just read what he said to do and dont worry :bigthumb:

so basically it's not boost creep cuz his exhaust still isn't "free" enough.

i see... thanks for the clarification

damn rynberg is tearing it up, i just learned like 5 new things about the fd turbo systems lol

A little update here. I just took everything apart looking for a bad vac hose or something. This is what i found. The question is would this make my car overboost? The hose the leads to the CRV was cracked. See atached pic and tell me if this would cause overboost?
https://www.rx7club.com/attachment.p...hmentid=150197

anyone?

First I am no expert in rotary twin turbo system...to the best of my knowledge the CRV vent boost generated by 2nd turbo at 3000-4500 rpm. After 4500 rpm CRV closed to add secondary boost to primary boost.

What happen to boost if CRV doesn't vent pressure during pre-spin stage of secondary turbo?

With that broken hose...I would think the car would lose boost...not gaining.

I was thinking the same thing, but then i was thinking that the wastegate wouldn't be getting 10psi so it would compensate causeing overboost? Or am i retarted?

I think the loose hose might cause loss of boost as a simple boost leak when you're above 4500rpm.

If you suspect your wastegate solenoid isn't working right, you can cross over the hoses and connectors to switch the precontrol with the wastegate. It's only a 5 min test and if the boost changes you have a good idea the solenoid is at least partly at fault.

Since it's now the coolest time of year - did you ever watch the boost very closely before in cool weather? (When I bought mine in March, it was in the 30s and 40s and it was showing 11-12psi at times).

Dave

Well changing that hose did me no good what so ever. It's even worst know. My though of the wastegate overcompensating for the boost leak was WRONG. Just ran a test, boost went to 1.1 bar, so not good, right at 4500. I immediately let off. Dam it I don't know where to go now.

Well i'm at a stand still. I took everything back apart checked all my lines made sure everything is clamped and in the right place. I guess i'm just going to buy an electronic boost controler and do it that way. Unless anyone has some ideas to help me out?

Do you know for sure that the boost didn't reach these levels in similar weather before?

Dave

It was 65 today standard CA weather. I've driven it in weather as cold as 37 and it wasn't boosting more then 11psi. 1.1 bar is 16psi, that's WAY over what it should be even in cold weather. I'm at a lose, i'm getting a Apexi AVC-R boost controller. That should cure my problem but i was hoping i could fix it with out having to spend 400$ on a boost contoler. I'm not doing a manual on i don't trust them.

Hmm, yeah 16psi is very high. Inspect every line on the wastegate circuit and make sure none of them are loose or leaking. It starts at the primary elbow, runs into the actuator, up into the vertical hard pipes, and into the wastegate solenoid. Also be sure the actuator is hooked to the wastegate valve and moving properly. If possible, use a Mityvac and be sure it passes the FSM test. Disconnect the wastegate solenoid, and make sure you can blow air through it.

If all that passes, try running with the wastegate solenoid electrical connector unplugged. It should limit boot to 8psi or so, and confirm that either the solenoid needs replaced. (Or it's time to go EBC).

Dave

As a temporary fix, you can remove the pill from the wastegate line. This will limit your boost, and allow you to drive the car. Might be a good idea if you still have things apart.

Good luck :)

If anyhting I would say that would cause you to lose boost... I blew out one of my houses on the turbo manifold and under boost the hose would open up and I would only be able to build 7 psi

fyi I had the same problem with my fd. The more mods I added the higher the boost spiked during secondary